Purpose: The presence of hip prostheses results in significant image artifacts making delineation of anatomy for planning difficult with traditional kilovoltage CT images. This report presents the use of megavoltage computed tomography (MVCT) imaging acquired with a helical tomotherapy unit to plan a high-dose-rate (HDR) prostate brachytherapy treatment for a patient with bilateral hip prostheses.
Methods and materials: A 77-year-old man presented with a localized clinical Stage T3a, Gleason 7 prostate cancer. Past history was also significant for bilateral hip prostheses. Staging workup included a negative bone scan and CT of abdomen and pelvis. The pelvic CT exhibited significant streak artifacts obscuring the prostate. HDR monotherapy with adjuvant androgen deprivation therapy was proposed. On the day of the implant and after catheter insertion, MVCT imaging of the pelvic area of the patient was obtained using a commercial helical tomotherapy unit. The MVCT images were transferred to Nucletron PLATO (v14.3.2) for planning with optimization of catheter dwell positions and times.
Results: MVCT images acquired with the helical tomotherapy unit allow good visualization of bony anatomy and of the hip prosthesis. No reconstruction streak artifacts are visible in the images as seen in the diagnostic kilovoltage CT images. Sufficient soft tissue contrast exists to allow delineation of the bladder and rectum. The absence of streak artifacts provides good quantification of Hounsfield number in the region surrounding the hip prosthesis and allows for good dose quantification.
Conclusions: MVCT images obtained using the commercial helical tomotherapy unit have been shown to provide good soft tissue contrast and no streak artifacts when planning a patient for prostate HDR brachytherapy having bilateral prosthetic hip replacements. The rectum and bladder can be clearly seen in the MVCT images and contoured independently. Prostate delineation is assumed from the position of the brachytherapy catheters.